Wayne,
This has come up before on a forum (I think it may have been Clean Talk because I think John Bolton answered it. I may be wrong though).
He suggested that the cleaner approach it like this...
"It is true, that very occasionally, in a handful of cases wordwide, that some sensitive people may be affected by something in the cleaning process.
This will show as a topical type rash ie Only on the parts that have contacted the carpet such as hands or feet.
If it is anywhere else, then you will find the problem has originated somewhere else".
I'm not sure word for word and apologies if it was someone other than John.
In other words, you are taking them seriously and helping but ruling yourself out of the equation.
I hope that helps,
Garry